1. Field of the Invention
The present invention relates to an ion implantation method and a device using thereof. More particularly, the present invention relates to an ion implantation method and a device using thereof having an excellent uniformity of implantation.
2. Description of Related Art
In the manufacturing process of semiconductor device, in order to obtain a predetermined conductivity, it is usually to add impurity to the film layer of the device, wherein the process is general called doping or implantation process and the impurity is called a dopant. The conventional doping method may be generally classified into diffusion method and ion implantation method. In general, the diffusion method is also called thermal diffusion method since the process is performed by the diffusion of the dopant in the host material from high dopant concentration area to low dopant concentration area under high temperature (generally about 800° C.). However, the ion implantation method is performed by accelerating and implanting the ionized dopant to dope the dopant into the host material directly.
FIG. 1 is a schematic cross-sectional view illustrating a conventional ion implanter. In general, the structure of a conventional ion implanter is quite complex. Referring to FIG. 1, the ion implanter 100 substantially comprises ion beam 102, ion source 104, mass analyzer 106, accelerator 108 and scanner 110. The ion source is used for generating the ion beam 102, and the mass analyzer 106 is used to separate and select a portion of the ion beam 102 to be used as the dopant. The accelerator 108 is used for accelerating the ion beam 102, and the scanner 110 is used for scanning the wafer 112 by the ion beam 102. Hereinafter, the problem generated in the conventional ion implanter will be discussed.
FIG. 2 is a top view schematically illustrating the method of scanning a wafer in a conventional ion implanter. As shown in FIG. 2, the ion beam is enlarged before the ion beam 102 is scanned over the wafer 204. Therefore, an ion beam area 202 is achieved. The size of the ion beam area 202 is adjusted in comparison with the size of the wafer 204, and the ion beam 202 is scanned along a scan path such as the zigzag path shown in FIG. 2 to be implanted in the whole area of the wafer 204. However, as shown in FIG. 2, in the conventional scan process, a portion of the wafer 204, for example, the area 206 is scanned at least twice. Alternatively, another portion of the wafer 204, for example, the area 208 is not scanned.
In order to solve the problem described above, conventionally the speed or frequency of scanning process is fixed to enhance the scan uniformity. Alternatively, the scanning speed is dependent on the ion beam current. Sometimes the times of scanning process are also increased. However, the improvement of the uniformity is not obvious. Alternatively, the thermal diffusion method is also adopted to improve the scan uniformity. However, the thermal budget of the whole process is increased, therefore the cost and process time are also increased.
In addition, when the ion beam is enlarged during the scanning process over the wafer to obtain the ion beam area 202, in general the ion concentration distribution on the ion beam area 202 is not uniform. Especially, the ions are mutually repelled since the ions in the ion beam have the same charges. Therefore, the ion beam is broad up during the scanning process, thus the shape of the ion beam is changed and the ion concentration distribution on the cross-section of the ion beam is not uniform. Therefore, the size, the shape and the ion concentration distribution of the ion beam area 202 has to be adjusted frequently during the scanning process.
Moreover, during the ion beam is implanted to the wafer and after the ion beam area 202 is formed, since the implanted ions are positively charged, the surface of the wafer are also positively charged. Therefore, the ion beam and the surface of the wafer are mutually repelled, and thus the position, size, shape and ion concentration distribution of the ion beam area 202 formed in the later implantation process. In general, the problem may be solved by applying an electron beam to the surface of the wafer to electricity neutralize the surface of the wafer. The electron beam is generated, for example, during the ionization of the ion beam. However, the influence of the implantation of the electron beam on the surface of the wafer has to be noted.
Accordingly, a method and device for effectively increase the uniformity of ion implantation process is quite desirable.